The real reason why PVP is imbalanced
SE dropped the ball on this one. They allow premade groups of 2 or 3 to join the duty finder for the non-premade match.
If they did it right, they would've made it so you can only join the non-premade match as a solo player. And make it so that you can only join the premade group match in a party of 2 or 4. Make it impossible to Duty Finder as a party of 3.
Anybody who forms a party of a SMN, BLM, and SCH will win almost everytime because they'll have a high chance of facing a non-premade group and that setup is almost fail proof.